Surface-enhanced Raman spectography (SERS) is one of the most promising detection techniques for identifying and characterising molecules. This technique consists in depositing the molecules of interest on a substrate that has a rough metal surface. The metal surface whereon the molecules of interest are fixed is then illuminated by a monochromatic light. The molecules then emit a Raman signal characteristic of these molecules, which makes them able to be detected and identified.
However the Raman signal emitted by the molecules has an intensity that is much less than the intensity of the monochromatic light with which the molecules were illuminated.
In order to overcome this problem, it has been observed that the roughness of the metal surface of the substrate that carries the molecules of interest makes it possible to enhance the Raman signal emitted by the molecules of interest thanks to the excitation of localised plasmons of the metal (enhancement via electromagnetic effect) and by transfer of charges between the metal and the molecule adsorbed (chemical effect). This enhancement makes it possible as such to specifically detect adsorbed samples with extremely low concentrations and/or over very short periods of time.
This enhancement can be accomplished thanks to “hot spots”. These hot spots are zones of the substrate where the electromagnetic field is localised and intense. For this, hot spots generally have dimensions that are less than the wavelength of the incident monochromatic light.
Prior art as such knows methods that make it possible to carry out hot spots on the surface of a substrate. These hot spots can be formed by cavities or by point effects. As such, the document Appl. Phys. Lett. 97, 063106 2010, Nanoletters, 9, 4505, 2009 describes hot spots formed by points. The document Nano Lett. 11, 2538, 2011; J. Vac. Sci. Technol. B 27, 2640 (2009) describes hot spots formed by cavities. However, the methods for forming hot spots of prior art use structuring technologies that can reach very high spatial resolutions and they are therefore complex and very expensive. Furthermore, they do not generally make it possible to produce substrates that have a high density of hot spots, in such a way that the increase in the light intensity emitted by the molecules of interest is limited.